On the morning of May 24, 1987, sometime after 1:30 A.M., a 23-year-old Canadian named Kenneth Parks drove 14 miles to his in-laws' home, strangled his father-in-law to the point of unconsciousness, and beat and stabbed his mother-in-law to death. A year later he was acquitted of both assault and murder. After a careful investigation, specialists reached the astonishing conclusion that Parks had been sleepwalking—and sleep driving and sleep attacking—during the incident.

This story inspired a 1997 made-for-television movie, The Sleepwalker Killing, starring Hilary Swank as Parks's wife. Although such extreme cases are rare, unintended acts of violence during sleep are quite common among those with sleep disorders. In a 1995 study of 64 sleep clinic patients suffering from sleepwalking or sleep terrors, more than half exhibited harmful behavior during sleep. An analysis at a different clinic that same year concluded that 70 percent of their 41 sleepwalking patients acted in a potentially injurious way.